Electric heater



3 Sheets-Sheet l III H. A. SOVERHILL ELECTRIC HEATER INVENTOR grim y/iSal/011171- ATTOZNEYS Filed July 6, 1955 Feb. 22; 1938.

Feb. 22, 1932;.-

H. A.YSO.VERHILL ELECTRIC HEATER Filed July 6, 19:55

5 Sheets-Sheefi 2 um iimmmlnzm mmWWW 5 INVENTOR flamzyfl Saw/lull BYATTORNEYS Feb. 22, 1938. H. A. SOVERHILL ELECTRIC HEATER Filed July 6,1955,

5 Sheets-Sheet 5 Patented Feb. 22, 1938 PATENT. OFFICE ELECTRIC naa'raaHarvey A. Soverhill, Chicago, Ill., assignor to The American FoundryEquipment Company, Miahawaka, Ind., a corporation of DelawareApplication July 6, 1935, Serial No. 30,067

. 9 Claims.

The invention relates to electric heaters, and more particularly toelectric, forced draft air heaters. Such heaters usually comprisea gridor heating element and a motor driven fan for forcing a blast of airacross the heating element to dissipate-the heat and to circulate theair.

According to a preferred forih of the invention, the heating element orgrid may be circular or ring shaped in form, the circular body having aplurality of outwardly. extending radial flanges and a plurality ofinwardly extending radial flanges, certain of said inwardly extendingradial flanges meeting at the center. The circular grid may be cast andshrunk around a circular sheath-wire heater. Such a sheath-wire heatermay comprise an outer tubular sheath having powdered insulating materialtherein in which is imbedded a helical resistance wire through which the"electricity is passed-to generate the heat. A cylindrical tube orshroud may surround the circular gridand the fan may be disposed withinthis shroud so that all of the air discharged by the fan is constrainedto pass through the grid and is available for cooling the convectionsurface of the grid. The motor driven fan and grid, together withsuitable electric control devices, may be mounted in a suitable casing.

The invention also consists in certain new and original features ofconstruction and combinations of parts hereinafter set forth andclaimed.

Although the novel features which are believed to be characteristic ofthis invention will be particularly pointed out in the claims appendedhereto, the "invention itself, as to its objects and advantages, and themanner in which it may be carried out. may be better understood byreferring to the following description taken in connection with theaccompanying drawings forming a part thereof, in which Fig. l is a frontview of the heater;

Fig. 2 is a vertical section on the line 2--2 of Fig. 1;

Fig. 3 is a vertical section on the line H of Fig. 2;

Fig. 4 is a horizontal section on the line 4-4 of Fig. 1;

,' Fig. 5 is a horizontal section on the line 5-5 Fig. 6 is a frontelevation of the grid; and

Fig. 7 is a side elevation of the grid partly in I section.

In the following description and in the claims, various details will beidentified by specific names for convenience, but they are intended tobe as ticularly to Figs. 1 to 5, the heater comprises a casing l0 havingdisposed therein a heat generating grid ll, fan l2, driven by motor It,service switch It and safety switch ii.

The casing I0 is made up for the most part of suitable sheet metal. Itcomprises a front plate It and back plate l9 suitably secured to aU-shaped plate forming sides 20 and 2| and top 22. The front and backplates are provided with large openings into which screens 23 and 24 aresuitably secured and the top 22 is provided with a handle 25 forconvenience in moving the heater from place to place. 1

The front l8 and back I! are secured to the sides and top 20, 2| and22in any desired manner. In the form shown for illustration, the frontand back l8 and I9 are provided with a peripheral flange in which thesides 20' and 2| and top 22 fit. Suitable welding or solder may beprovided for holding the parts of the casing in assembled relation.

The legs 26 are formed by cutting out large recesses or notches in thesides 20 and 2| and front i8 and back is. Reenforcing these legs aretubes 21 suitably secured in position, in the lower ends of which arerubber plugs 28 held in position by compressional stress of nuts andbolts 28 passing therethrough. The legs thus made are sturdy and therubber plugs 28 prevent marring of any surface on which the heater maybe placed.

The casing may be provided with a bottom plate 3i which may be suitablysecured, as by detachable screws, to flanges 32 bent inwardly from thefront, back and sides of the. casing. The service switch it is suitablysecured to the back is with the finger-engaging tumbler projecting outthrough the casing. The safety a switch l5 may be also suitably securedto the inside of the back i9 with its knob projecting through to theoutside of the casing.

7 All of the enclosed apparatus is mounted on a pair of threaded rods 34passing through the front and back of the casing. The grid ll isprovided with a pair 01' long lugs 33. The motor I 3 supporting the fanI Z-is mounted on a suitable side of the circular grid II and has itsear end slightly flared. Within this flared portion, fan

l2.has a close running fit, so that all of the air discharged by the fanmust pass through the grid. The switch. I 4 is the ordinary serviceswitch and may control both the motor i3 and the heater element H. Thesafety switch It includes a rod 37 surrounded by a safety heating coil36. The construction and operation of the safety switch I5 is' explainedmore in detail in my Patent No. 2,061,258, issued November 17, 1936.

Referring now to Figs. 6 and 7, the grid it comprises a pair ofsheath-wire elements 40. Each sheath-wire element comprises a metallicsheath 4| having powdered insulating material 42 therein. Imbeddedwithin the insulating material is a coiled resistance wire 43. Theelectric insulating material 42 is high heat conducting and is packedtightly within the tubular sheath 4|, as will be understood by thoseskilled in the art.

The grid II also includes a jacket 46 of aluminum or other high heatconducting material. The jacket 46 comprises a circular or tubular body41 with outer radial heat dissipating flanges 48 and inner radial heatdissipating flanges 49, 50 and 54. Certain of these inner flanges 5|meet at the cent-er forming a unitary construction for a purposehereinafter described more in detail.

The sheath-wire elements 40 are cast within the body 41 during theprocess of manufacture so that the grid 1 I forms a perfect heatconducting unit from the resistance wire 43, where the heat isgenerated, to the convection surface on the heat dissipating ribs orflanges. Thus, this construction permits the dissipation of immensequantities of electric energy within a small geometrical space.

A certain part of the jacket 46 is arranged for the binding posts 44.These binding posts have their shanks projecting into the sheath-wireele- -ments to limit the generation of heat to'those parts of thesheath-wire elements closely sur- Insufrom the surrounding metal 4i andjacket body 41.

The electrical connections of the motor, switches and sheath-wireelements may be made in any desired manner.

upon the voltage rating of these elements and on the voltage with whichthe heater is to be used.

In operation, when voltage is applied to the sheath-wire elements 40,the grid It will be heated. The operation of the motor 53 driving fan l2draws air from the room in through the rear screen 24, discharging itthrough the-shroud Iii and grid H, through the front-screen 23.

A sufficient quantity of air is supplied to keep the temperature of thesurface of the grid I 5 down to comparatively low values, as forexample, 250 F. The bowed. shape of the screens 23 and 24 assists inincreasing the area from which the air is drawn and also assists indiffusing the air In certain cases, thetwo sheath-wire elements may beconnected in series and in other cases in parallel, depending forced outof the heater, as indicated by the arrows in Fig. 2.

The sheath-wire heater elements 40 are operated at very high heatdissipating densities, as

for example, watts per square inch of surface of. the sheath 4!. Thiscompares with the ordin'ary operation of sheath-wire heaters, when usedalone in a blast of air, of about 10 watts per square inch of sheathsurface. Because of the extremely high dissipating density, it isimportant that all parts of the jacket 46 be subjected to equal cooling.Accordingly, the convection surface of that part of the jacket lyingoutside of. the center line of the body 41, including the ribs orflanges H, is made substantially equal to the convection surface on theinside of the center line of the body, including principally the flanges49, 50 and Si. Extending the flanges 5| to the center assists inproviding this equal distribution of convection surface and also assistsin making a stronger casting. 7

According to the invention, the resistance of different parts of thegrid to air flow is made substantially uniform. Also the fan I! ispreferably designed to give substantially uniform velocity to the airblast throughout the entire cross sectional area of the air blast. Theshroud 30 insures that substantially all of the air'must sweep theconvection surface of the grid. These factors, together with theequalized convection surface with respect to the heat generatingsheathwire elements, provide an arrangement by which immense amounts ofheat may be dissipated with a heater of small geometrical dimension.

A further advantage of the invention is that only one grid casting isrequired for a single heater. Also, only ,one type of sheath-wire heateris required. One sheath-wire heater may be used, or two, as in the formillustrated, or, if desired, three or more sheath-wire heaters may beused. In some cases, a single sheath-wire heater may be used having aplurality of circular convolutions. In any event, care should be takenin spacing the adjoining sections of sheath-wire heater from each otherto provide a sufficient parts of sheath-wire heater are disposed tooclosely, the Jacket will not properly flow in between during the castingprocess, causing an air pocket at this point, which is fatal to theoperation of the heater.

The provision of a comparatively low surface temperature on the grid ofthe heater assists in increasing the capacity of the heater by keepingthe temperature gradient from the resistance wire, where the heat isgenerated, to the convection surface of the grid at a maximum. The airleaving the heater is not sumciently hot to scorch anything with whichit comes in contact. be seen that the ratio of convection surface to thesurface of the sheath-wire heater is greatly increased. This ratio maybe of the order of 18 or 20 to 1. This greatly extended convectionsurface, together with a suiiicient air velocity, which may run as highas 800 feet per minute in ordinary requirements, and sometimes up to1500 feet per minute for special purposes, permits great amounts ofenergy to be dissipated.

While certain novel features of the invention have been disclosed andare pointed out in the annexed claims, it will be understood thatvarious omissions, substitutions and changes may be made by thoseskilled in the art without departing from the spirit of the invention.

What is claimed is:

1. In a heater, an annular heat generating grid comprising a cylindricalbody having outwardly extending and inwardly extending, radial, heatdissipating fins, certain of said inwardly extending fins meeting in thecenter, and a motor driven fan spaced axially from said grid formaintaining a column of air therebetween.

2. In an electric heater, a casing, an ann heater grid in said casing,said grid comprising a single-wire, sheath-wire, heater element, ajacket cast around said heater element and comprising a thin cylindricalbody enclosing said heater element and having radial fins extendingoutwardly from said body and second radial fins extending inwardly fromsaid body, certain of said inwardly extending radial fins meeting at apoint in the center, a motor having a fan thereon in said casing, theheat dissipating surface of that part of said grid extending inwardlyfrom the midpoint of said body being substantially equal .to that partextending outwardly from the midpoint of said body.

3. In an electric heater, a casing, an annular heater grid in saidcasing, said grid comprising a sheath-wire heater element, a jacket castaround said heater element and comprising a thin cylindrical bodyenclosing said heater element and having radial fins extending outwardlyfrom said body and second radial fins extending inwardly from said body,certain of said inwardly extending radial fins meeting at a point in thecenter,

a motor having a fan thereon in said casing, the heat dissipatingsurface oi that part of said grid extending inwardly from the midpointof said body being substantially equal to that partextending outwardlyfrom 'the midpoint oi said I I 4. In an electric heater, a casingcomprising a front wall, a back wall and a U-shaped wallsecuredtheretoformingsidewailsandtopwall, said front and back wallshaving outlet and inlet openings, respectively, screens in said openingsvfor concentrating theintakeairanddiifusingthe outlet air, a pair ofhorizontal rods on opposite side passing through the back and frontwalls, an electricheat generating gridmounted on and'betweensaidrods,asaddlemountedonandbetween said rods, a motor restingon said saddle and supporting a fan, and a cylindrical shroudsurrounding saidcircular grid and said fan.

5. In a unit-heater, a casing comprising afront wall, a back wall, aU-shaped wall secured thereto forming side walls and top wall, aseparate bottom wall secured to certain of said aforesaid walls, saidfront and back walls having outlet andinlet openings, respectively,screens in said openings. a heat generating unit in said casing,

amotorsimportingafaninsaidcasingformaintainingacolumn ofair throimh saidopenings -andsaidunit.

6. In an electric heater, a casing, an annular heater grid in saidcasing. said grid comprising a plurality of separate, ring shaped,single-wire,

sheath-wire hea er e ement a r g Bide W heat dissipating surface of thatpart of said grid extending inwardly from the midpoint of said bodybeing substantially equal to that part extending outwardly from themidpoint of said shell, .said fan being coaxial with said grid, the

body and the velocity of the air discharged. by

said fan being substantially uniform throughout all parts of the grid.

'I. In an electric air heater, an annular grid comprising an annularjacket, electric heat generating elements within said jacket, saidJacket being cast around said electric heat generating elements, outerheat dissipating fianges extending outwardly from said jacket, innerheat dissipatingfianges extending inwardly from said jacket andutilizing substantially the entire heat dissipating space within saidjacket, and a fan adjacent said grid for directing a stream of air oversaid grid.

8. In an air electric air heater, an annular grid comprising an annularjacket comparatively thin in section, electric heat generating elementswithin the body of said Jacket,- said jacket being cast around saidelectric heat generating elements, outer heat dissipating fiangesextending outwardly from said jacket, inner heat dissipating fiangesextending inwardly from said jacket and utilizing substantially theentire heat dissipatingspaeewithinsaidgiacketanannularwall surroundingand adjoining the outer edges of saidouterfiangeaafaii adiacentandwithinssidannularwalLthemedialsurfacesofssid Jacket, fianges and outer wallextending parallel with the direction of air flow.

9.Inaneiectricairheater,anannulargrid comprising an.annular jacket, anelectric, heat generating, sheath-wire heating unit comprising ametalsheath,asingleresistancewiredisposed within said sheath, electricinsulating, heat conductingmaterialpackedwithinsaidsheath'sroundsaidwiresaidannularjacketbeingcast around said heating unit, outerheat dissipating elements cast integrally with said jacket and extendingoutwardly from said jacket, inner heat dissipating elements castintegrally with said jacket and extending inwardly from said jacket, anannular wall surrounding andadiacent the"

